Generate random string in pure C WinApi

gen_rand_str.c

#include <windows.h>
#include <ntsecapi.h>
#include <stdio.h>

DWORD random_num(DWORD min, DWORD max)
{
   if (min > max)
       return 0;

   DWORD val;

   if (!RtlGenRandom(&val, sizeof val))
       return 0;

   DWORD t = max - min + 1;

   if (0 == min && ~0UL == max)
       --t;

   return val % t + min;
}

PCHAR random_chars(PCHAR b, DWORD n)
{
   for (DWORD i = 0, j; i < n; ++i) {
       j = random_num(0, 2);

       b[i] = "0aA"[j] + random_num(0, j ? 'z'-'a' : '9'-'0');
   }

   return b;
}


void main(void)
{
   CHAR s[32 + 1] = { 0 };

   for (int i = 0; i < 32; ++i)
       printf("%s\n", random_chars(s, sizeof(s)-1));

   ExitProcess(0);
}